It might be a little late to comment on this, but here at Atma-Sphere we use an old school means of defining feedback:
A cathode or emitter resistor is a form of negative feedback called *degeneration*. This form of feedback occurs in real time and also has the effect of increasing the output impedance of the circuit. A secondary form of degeneration is the type where a push-pull amplifier can cancel even-ordered harmonics in its output. In any case the feedback is characterized by being in exact real-time opposition to the output signal.
The second type, the 'bad' kind IMO, is *loop* or *global* feedback and is the more common variety referred to loosely as negative feedback. In this form, a portion of the output signal of an amplifier circuit is applied back to the input of the circuit (and can be tube, transistor or opamp). Due to propagation delays in the amplifier circuit itself, the weakness of this approach is to be increasingly less correct as the frequency increases, and/or less accurate as the propogation delay through the circuit is increased. IOW it is not in real-time opposition to the signal. Generally the output impedance is said to be lowered with this type of feedback.
I personally do not like loop feedback as it increases odd-ordered harmonics (depending to certain degree on the amplifier circuit too) in the range at or beyond *about* the 9th harmonic up the 17th- the area that the human ear (over millions of years) has evolved to use to detect loudness. Obviously we cannot change our ears! IOW, these harmonics make an amplifier sound louder and harsher, and they only need be in vanishingly small amounts to be noticed. Humans are *very* sensitive to this type of distortion.
I feel that the appearance of low and 'zero' feedback amplifiers ('zero' meaning zero loop feedback) in the last two decades is a good thing. Negative feedack is a character of the ruling Voltage test and measurement paradigm, which has been in place for some 50-60 years. It has been responsible for a lot of foolishness over that time, negative feedback's acceptance being one of them.
The opposing paradigm, the Power paradigm, uses slightly different rules of test and measurement, which conform more closely to the rules that the human ear has developed over the millennia. Horn speakers, ESLs and magnetic planar speakers all operate according to the power paradigm. So these zero feedback amplifiers that have appeared have some venerable company...
Back to our regularly scheduled flames, already in progress :)
A cathode or emitter resistor is a form of negative feedback called *degeneration*. This form of feedback occurs in real time and also has the effect of increasing the output impedance of the circuit. A secondary form of degeneration is the type where a push-pull amplifier can cancel even-ordered harmonics in its output. In any case the feedback is characterized by being in exact real-time opposition to the output signal.
The second type, the 'bad' kind IMO, is *loop* or *global* feedback and is the more common variety referred to loosely as negative feedback. In this form, a portion of the output signal of an amplifier circuit is applied back to the input of the circuit (and can be tube, transistor or opamp). Due to propagation delays in the amplifier circuit itself, the weakness of this approach is to be increasingly less correct as the frequency increases, and/or less accurate as the propogation delay through the circuit is increased. IOW it is not in real-time opposition to the signal. Generally the output impedance is said to be lowered with this type of feedback.
I personally do not like loop feedback as it increases odd-ordered harmonics (depending to certain degree on the amplifier circuit too) in the range at or beyond *about* the 9th harmonic up the 17th- the area that the human ear (over millions of years) has evolved to use to detect loudness. Obviously we cannot change our ears! IOW, these harmonics make an amplifier sound louder and harsher, and they only need be in vanishingly small amounts to be noticed. Humans are *very* sensitive to this type of distortion.
I feel that the appearance of low and 'zero' feedback amplifiers ('zero' meaning zero loop feedback) in the last two decades is a good thing. Negative feedack is a character of the ruling Voltage test and measurement paradigm, which has been in place for some 50-60 years. It has been responsible for a lot of foolishness over that time, negative feedback's acceptance being one of them.
The opposing paradigm, the Power paradigm, uses slightly different rules of test and measurement, which conform more closely to the rules that the human ear has developed over the millennia. Horn speakers, ESLs and magnetic planar speakers all operate according to the power paradigm. So these zero feedback amplifiers that have appeared have some venerable company...
Back to our regularly scheduled flames, already in progress :)